The invention relates generally to techniques for mitigating the effects of arcs, and more particularly to arc containment.
An arc flash may be defined as a condition associated with the release of energy caused by an electric arc. This release of energy is in the form of light and heat, often causing a pressure or shock wave. Arc flashes occur when the insulation between two conductors (often only air) can no longer withstand the voltage between them, resulting in an insulation breakdown. The energy produced by an arc flash event is a function of the voltage between the conductors, current flow during the event, and the duration of the event. To reduce or mitigate the deleterious effects of these events, design engineers have options such as grounding practices and current limiting fuses to reduce system voltage or fault currents. However, under certain conditions reducing arc fault clearing time is another approach to reducing the let-through energy resulting from the arc fault.
When arc flashes are contained, high energy levels released can involve very high pressure waves, on the order of tens to hundreds of bar, the transient and ultimate pressures of which depend upon the magnitude of short circuit current, and the volume and nature of a container. Consequently, the cost of the container increases exponentially with the magnitude of current. Shock waves are generated due to instantaneous heating of the gas or vaporized components around the arc. Pressures created by the shock wave may also be quite high, on the order of hundreds of bar, and are a function of the current magnitude and distance of the container wall from the arc. The shock waves occur during initial stages of arc formation. The ultimate pressure resulting from the expanding gas builds inside the container, and is generally a function of such factors as the duration of the event, the magnitude of the short circuit current and the volume of the containment chamber.
Therefore, there is a need for an arc containment approach designed to withstand both shock waves and high pressures with minimized size and cost.